The British Phonographic Industry (BPI) is threatening to sue individual music fans who swap song files over the internet.

This follows action by the Recording Industry Association of America (RIAA), which has sued 1,977 downloaders.

BBC News Online looks at what this could mean for music swappers around the world, and the issues behind the latest tactics.

I have downloaded music over the internet. Can I be sued?

Not if you have downloaded songs that have been put online with the approval of record labels and artists - which usually involves paying for royalties. Sanctioned services include Apple's iTunes and Napster in the US, plus MyCokeMusic, HMV and Virgin in the UK.

If you download unapproved tracks from unsanctioned sites - whether it is one song or a million - you are infringing copyright and you run the risk of being sued.

Could I be sued for swapping just a few songs?

Theoretically, you could. But the BPI says the problem stems from a small hardcore of "serial uploaders" who offer hundreds or thousands of music files over the internet.

The RIAA took action against a college student in Michigan who ran a network offering more than 650,000 files - the equivalent of more than 43,000 albums. They have chased other users who have again uploaded thousands of files.

Can children be sued for uploading or downloading songs?

The RIAA says it could prosecute anyone, including children. The BPI has not said if children will also be targeted.

Why are record companies so worried?

Music sales are falling, with global annual record sales down from $40bn (£22bn) to $30bn (£17bn) over the past four years.

The BPI says the amount UK downloaders spend on albums fell 32% between 2002 and 2003, and that their spending on singles was down 59%.

The music industry, which has suffered massive redundancies and restructuring in the last decade, says the swapping of music files over the internet is one of the major parts of music piracy. It has sued online song-swapping services like Napster, and is in the process of suing Kazaa.

Why is the BPI taking action now?

In 2003 the BPI said suing individual users would be a "last resort".

But recent research indicates that eight million people in the UK claim to be downloading music, 92% of them using illegal sites.

Why are they chasing individual users?

The music industry has had mixed fortunes in its court actions against the companies that support file-swapping on the internet. Some have been successful - like the action which forced Napster to close - and some have not.

Last year a US judge ruled that two file-swapping networks, Grokster and Morpheus, were not responsible for what was traded on their systems.

However, the RIAA was successful in getting telecommunications giant Verizon to hand over details of customers who swap files. This has allowed them to begin the process of gathering evidence against individuals.

Are other music industry groups going to take similar action?

Germany, Switzerland, Denmark, Spain and Italy have already taken similar action, says the International Federation for the Phonographic Industry (IFPI). German police impounded computer equipment in 2003 in the town of Furth that had been used to upload up to one million files. In Italy at least 75 actions have been taken.

Will legitimate online services ever rival the peer-to-peer sites?

The April 2003 launch of Apple system iTunes was a huge success, with more than five million songs downloaded in the first month. So far the service is only available in the US, however. Microsoft plans a similar online music service.

Coca-Cola's site Mycokemusic.com launched in Europe in January and said it attracted 700,000 visitors in its first two months.